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Lens review

2012-03-29
 

Sigma 30 mm f/2.8 EX DN

7. Coma, astigmatism and bokeh

On a small Micro 4/3 sensor the coma is corrected very well. The image of a diode positioned in the corner of the frame is only slightly distorted and in most cases this aberration won’t be bothersome at all.

Sigma 30 mm f/2.8 EX DN - Coma, astigmatism and bokeh

The situation with astigmatism looks a bit more serious. At the maximum relative aperture it is really noticeable, reaching 13%. It decreases a bit on stopping down the aperture to f/4.0 getting to about 10% there. It becomes imperceptible only by f/5.6.

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The images of defocused diode, shown below, are hardly perfect too. The light is spread out in distinct ring shapes which suggest some mild problems with the spherical aberration correction.

Sigma 30 mm f/2.8 EX DN - Coma, astigmatism and bokeh

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